Edge sharpener for skis

ABSTRACT

According to the present invention there is provided an apparatus for sharpening an elongate edge, especially the blade edge of a ski. The apparatus comprises an abrasive disc set in a housing, a motor unit for rotating the disc about its axis, a guide surface parallel to the plane of the disc, guide means defining a guide plane substantially at right angles to the guide surface, and means to bias the disc axially to a position just proud of the guide surface.

This invention relates to apparatus for sharpening edges, particularlyto such apparatus adapted for sharpening the edges of skis. It can,however, be used for sharpening other edges if desired.

The base of a modern ski has two metal edges on its lower surface. Inorder for the skier to be able to turn satisfactorily, especially on icesurfaces, it is necessary that these edges are sharp. This isconventionally done by skilled personnel carrying out ski sharpeningservices in association with the sale of skis and ancillary ski-ingequipment.

The ski-owner can sharpen his own skis if he has a suitable tool fordoing so. A known tool consists of a short metal file set in anL-section holder provided with a handle. The user moves the holder alongthe ski edge with the file at the side of the ski. This known implementis not very easy to use to give good results.

Other types of hand-held or hand operated ski sharpening tools are knownbut these also do not produce satisfactory results.

Electrically operated ski sharpeners are known in which a grinding wheelis driven by an electric motor, the grinding wheel being mounted on theoutput shaft of the motor. In French Patent Specification 2516004, theski sharpener disclosed is operated by moving the rotating grindingwheel along the edge of the ski, means being provided to guide the wheelas it is moved along the edge. In this sharpener, it is not possible toadjust the amount of material removed as the device is moved along theedge. If a large amount of material is to be removed, the device has tobe used several times to achieve that result.

European Patent Specification 0058983 discloses another ski sharpeningdevice. In this device, the motor is pivotally mounted about an axistransverse to the motor axis which allows the motor limited angularmovement about that axis. A compression spring is used to bias the motorwithin a housing to a position where the motor axis forms a small angleto the motor axis position when the device is operating. This smallangle is typically 2° to 3°. The biasing force of the spring is overcomeby the reaction between the edge of the ski and the grinding wheel sothat the motor can only be operated when the motor axis is correctlyaligned. The sharpening device is held against the edge of the ski andguide means are provided to assist movement of the device along theedge. The amount of material removed from the edge can be varied byaltering the biasing force exerted by the spring on the motor.

In the electrically operated ski sharpening devices described above, thecircumferential surface of the grinding wheel is used to sharpen theedges, and because the whole grinding surface of the wheel tends not tobe used and hence is worn away unevenly, the grinding surface has to bedressed frequently in order to optimise the grinding performance of thewheel to produce satisfactory results.

According to the present invention there is provided apparatus forsharpening an elongate edge, especially the blade at the edge of a ski,comprising an abrasive disc set in a housing, a motor unit for rotatingthe disc about its axis, a guide surface parallel to the plane of thedisc, guide means defining a guide plane substantially at right anglesto the guide surface, and means to bias the disc axially to a positionjust proud of the guide surface.

Advantageously, the motor unit includes an axially adjustable spindle onwhich the disc is mounted. The position of the spindle may be adjustedwithin the motor unit by means of a set screw and lock nut arrangement.The means for biasing the disc may comprise a compression spring mountedin the housing which acts on the disc to move it away from the guidesurface.

Alternatively, the motor armature carried by the spindle can be axiallymovable and urged by magnetic forces between the armature and motorhousing to cause the abrasive disc to be moved away from the guidesurface.

Preferably, the guide means comprises a pair of rollers, one positionedon each side of the motor unit, the surfaces of the rollers defining aguide plane which is tangential to the rollers.

Each roller may be attached at one end to the guide surface and be freeat its other end.

It is possible to use the sharpener of the invention to sharpen the edgeso that it has an included angle of just less than 90°. This can beachieved by tilting the ski with respect to the sharpener. In oneembodiment, adjustment can be provided by a set of O-rings which arepositioned in grooves on the rollers. The angle of deviation from 90°can be determined by the position of the O-rings relative to the guidesurface, for example, the further away the O-rings are from that surfacethe smaller the angular deviation from 90°. Alternatively, an adjustablestrap can be used to guide the ski relative to the guide surface.

It is preferred that the disc has an abrasive diamond surface, but anyother abrasive material can be used.

For a better understanding of the invention, reference will now be madeby way of example only to the accompanying drawings, in which:

FIG. 1 is a view of a ski-sharpener unit seen from below,

FIG. 2 is a sectional view along the lines X--X on FIG. 1,

FIG. 3 is an end view seen in the direction of Arrow Y on FIG. 1, and

FIG. 4 is a part sectional view of a further embodiment of theinvention.

Referring to the FIGS. 1 to 3, the unit has a generally cylindricalhousing 1 having a transverse endpiece 2 fixed to one end by a pair ofbolts 3.

Attached to endpiece 2 at either side of housing 1 is a roller 4extending parallel to housing 1. Two different sorts of roller areillustrated in FIG. 1, but in practice the rollers would match, beingeither a stud 5 bearing a free-running roller sleeve 6, or a longer stud7 bearing a free-running roller sleeve 8 of somewhat differentconfiguration from sleeve 6.

The surfaces of the two rollers 4 define a guide plane tangent to therollers and which is at right angles to a guide surface 9 of endpiece 2.A ski or other elongate blade to be sharpened can thus be locatedrelative to the unit by resting it on rollers 4 and aligning its edgeagainst the guide surface 9. The edges 10 of the ski would lie whereshown by dashdot lines in FIG. 1. In practice, the unit would be laid onthe upturned ski, rather than laying the ski on the unit.

The exterior of cylindrical housing 1 is cut away to give a flat face 12as shown.

Inside housing 1 is a motor unit 20 (as shown in FIG. 2). The armatureof the motor carried by spindle 28 can move axially in bearings, and itsprecise position is controlled by end bushes 21, 22. The position of endbush 21 is set by a set screw 23 and lock nut 24, screw 23 beingthreaded in one end cap 25 of housing 1.

Bush 22 is set in an opposite end cap 26 and is biased toward the motorby a compression spring 27. Bush 22 presses not directly on the spindleof the motor but on one face of an abrasive disc 30 set on the spindleand secured by a grub screw 31.

Disc 30 has an abrasive surface 32, preferably formed by attachingdiamond abrasive to the disc face, though other abrasive materials canbe used if desired. Diamonds, e.g. diamond chippings of grit size 120 to220, are preferred, with a grit size of 160 being a suitable compromisebetween too coarse (which would not sharpen as well and which wouldremove an excessive amount of the blade at the ski edge) and too fine(which would sharpen very well, but take a long time).

Power for the motor is fed in by an electrical lead 40. When the motoris activated disc 30 turns and the edge of the ski located at 41 isabraded by abrasive surface 32. The pressure which the disc 30 exerts onthe edge is controlled by spring 27, so the user cannot overgrind theski edge. As the unit is placed on the ski to sharpen the edge, and theedge of the ski brought to lie against guide surface 9, the whole motorarmature and spindle 28 moves slightly to the right as shown in FIG. 1,bringing the abrasive surface 32 of disc 30 from a position just proudof surface 9 to being flush with it. When so placed on the ski, themotor is actuated and the unit slid along the ski until the desiredsharpening has been achieved.

Instead of using the spring 27 to bias the disc against the edge to besharpened, magnetic forces in the motor itself can be employed.

For each motor, there is an axial position of the armature within themotor housing to which the magnetic forces urge the armature. If thearmature is moved from that axial position relative to the housing,there is a net magnetic force tending to move the armature back to thatposition. This net magnetic force can be used to provide the biasing ofthe armature so that the disc 30 can exert a controlled cutting force orcutting pressure on the edge of the ski.

The force of gravity can be used in combination with this magneticeffect to vary the amount of cutting pressure applied to the edge of theski. FIG. 4 illustrates how this can be effected.

FIG. 4 shows partly in section an alternative form of ski edge sharpeneraccording to the invention.

Referring to this Figure, a motor is located in a casing 60 which isattached to a guide plate 61. Set in casing 60 is an electric motorconsisting of an outer motor casing 62, fixed permanent field magnets63, and an armature 64 rotating on a spindle 65. Spindle 65 rotates insintered metal bearings 66 and projects into an aperture in guide 61.Mounted on the projecting end of spindle 65 is a disc 70 fixed inposition by a set screw 71. A protective cover 72 prevents access to thedisc when in place. At either end of the guide member 61 are freelyrotatable rollers 80, each of which has an O-ring 81 resilientlythereon. Rollers 80 are mounted on spindles 82 at the base of which,where the spindle is fixed to guide member 61, there is a thin steelshim 83 on guide member 61.

Shims 83 constitute the actual bearing surface against which the edge ofthe ski to be sharpened is placed when the sharpener is to be used.

The general arrangement of the abrasive disc 70 and guide rollers 80corresponds to the corresponding general arrangement as shown in FIGS. 1to 3 with respect to rollers 4 and disc 30.

Internally of the motor, the spindle carries at the end of armature 64 acommutator 67 cooperating with brushes 68 to which electrical power isfed in standard fashion. The end of the casing includes a switch 69.

The spindle 65 has a degree of axial float in the bearings 66. As can beseen from the drawing, permanent field magnets 63 are offset fromarmature 64 and thus accordingly bias the armature downwards as seen inFIG. 4.

The abrasive faced disc 70 is positioned with the aid of set screw 71 onthe end of shaft 65 such that its outer annulus of abrasive material,denoted 74 in FIG. 4, is in a plane a short distance downwardly as seenin FIG. 4 from the plane defined by the surfaces of shims 83. This shortdistance corresponds to the maximum depth of cut achievable in astraight edged blade abutted against shims 83.

Because of the axial free movement possible for the assembly of armature64, commutator 67 and shaft 65, when an edge is placed for sharpeningagainst shims 83, the working surface 74 lies coplanar with the surfacesof shims 83.

The working surface of the disc is, however, biased towards the bottomof the drawing shown in FIG. 4 and the amount of bias will determine therate at which, for a given rotational speed, the surface, e.g. of a skiedge held against shims 83 will be ground down.

It can be seen that the pressure of the abrasive face 74 of the disc 70against an edge to be sharpened which is laid abutting shims 83 will bemade up of two components, that is to say a force arising from themagnetic interaction between field magnets 63 and armature 64, and theforce of gravity acting on the assembly of armature, commutator, spindleand disc.

Thus, if the device of FIG. 4 is used with the axis of spindle 65horizontal, the bias with which the abrasive surface is pressed againstthe edge to be sharpened will consist solely of the magnetic forcecomponents. It may be increased by turning the assembly of ski to besharpened and sharpener so that the disc 70 is above the ski edge, withthe axis of spindle 65 vertical. This is the maximum force obtainableand will give the greatest amount of grinding over a given time. If, onthe other hand, all that is required is for the edge to be given a finallight sharpening polishing action, then the device may be used againwith its motor shaft 65 vertical but with the abrasive disc 70 below theblade edge to be sharpened. Obviously for this the magnetic forces mustbe capable of just slightly overcoming the gravitational forces.Clearly, by rotating the assembly, the pressure exerted by the abrasiveface 74 on the edge may be varied continuously.

It is sometimes desired to sharpen the blade to have an included angleof just less than 90°. This may be achieved with the unit of theinvention by tilting the ski slightly with respect to the unit, e.g. byan angle "B" as shown on FIG. 2. This may be achieved in controlledfashion by the use of an adjustable strap 50 set across surface 12 andwhich can be set to engage the bottom of the ski. Alternatively, rollers8 may have O-rings set in grooves in their circumferences. A set ofaxially spaced grooves on each roller 8 allows for fine adjustment. OneO-ring is shown at 51 for illustration. The further the O-rings are fromthe surface 9, the smaller the angle "B". In FIG. 4, O-rings 81 are seton rollers 80 for the same purpose.

The motor may be any convenient voltage. Particularly preferred is a 12V winding which may be provided with power from a vehicle battery (e.g.via a plug inserted into the cigar lighter socket) or from a mainsstep-down transformer unit. A typical motor power is 100 watts.

I claim:
 1. Apparatus for sharpening an elongate edge, especially theblade at the edge of a ski, comprising an abrasive disc set in ahousing, an electric motor for rotating the disc about its axis, a guidesurface parallel to the plane of the disc, and guide means defining aguide plane substantially at right angles to the guide surface, whereinthe motor includes an axially-movable spindle to which the disc isfastened, and a permanent field magnet positioned so as to apply forceon the spindle to bias the disc towards the motor at all times. 2.Apparatus according to claim 1 wherein the spindle movement towards themotor is determined by means of a set screw and lock nut.
 3. Apparatusaccording to claim 1 wherein the guide means comprises a pair of rollersand the surfaces of the rollers define a guide plane which is tangentialto the rollers.
 4. Apparatus according to claim 3 wherein each roller isattached at one end to the guide surface and is free at its other end.5. Apparatus according to claim 3 or 4 wherein each roller has aplurality of axially spaced grooves formed in its circumference forretaining an O-ring.
 6. Apparatus according to claim 1 furthercomprising a removable strap on the motor housing intended to engage asurface of the ski in such a manner as to tilt the ski edge so that theski edge meets the plane of the disc at an included angle of just lessthan 90°.
 7. Apparatus according to claim 1 wherein the disc has anabrasive diamond surface.